Dehydration of bituminous emulsion

ABSTRACT

A process for the thermal dehydration of a bituminous emulsion with heat from exhaust steam while simultaneously condensing the exhaust steam is disclosed herein. The process comprises heating a stream of bituminous emulsion by heat transfer from partially cooled steam turbine exhaust steam, to vaporize low boiling materials, principally water, and condense the steam, separating the vapor from the bituminous emulsion to partially dehydrate the emulsion, heating the partially dehydrated emulsion to a higher temperature by heat transfer from the exhaust steam of the steam turbine to vaporize the remaining water, and separating the water vapors from the bituminous stream. Preferably the turbine exhaust steam is first reheated and utilized to heat the fully dehydrated bitumen emulsion prior to subjecting the bitumen to solid-liquid separation by cycloning.

United States Patent Inventor Robert D. Hendry Edmonton, Alberta, CanadaAppl. No. 764,188

Filed Oct. 1, 1968 Patented Nov. 9, 1971 Assignees Canada-CitiesService, Ltd.

Calgary, Alberta, Canada;

Imperial Oil Limited; Atlantic Richtield Corporation; Royalite OilCompany Limited, part interest to each DEIIYDRATION 0F BITUMINOUSEMULSION 3 Claims, 1 Drawing Fig.

US. Cl 208/187 Int. Cl C10g 33/00 Field of Search 208/187, 188, 177

References Cited UNITED STATES PATENTS 1,983,832 12/1934 Bailey 208/187EMULSION Assistant Examiner-G. J. Crasanakis Attorney-J Richard GeamanABSTRACT: A process for the thermal dehydration of a bituminous emulsionwith heat from exhaust steam while simultaneously condensing the exhauststeam is disclosed herein. The process comprises heating a stream ofbituminous emulsion by heat transfer from partially cooled steam turbineexhaust steam, to vaporize low boiling materials, principally water, andcondense the steam, separating the vapor from the bituminous emulsion topartially dehydrate the emulsion, heating the partially dehydratedemulsion to a higher temperature by heat transfer from the exhaust steamof the steam turbine to vaporize the remaining water, and separating thewater vapors from the bituminous stream. Preferably the turbine exhauststeam is first reheated and utilized to heat the fully dehydratedbitumen emulsion prior to subjecting the bitumen to solid-liquidseparation by cycloning.

SOLIDS DEIIYDRATION OF BITUMINOUS EMULSION This invention relates to animproved process for the removal of water contained in a bituminousemulsion. More particularly, this invention relates to a process forefficiently utilizing the latent heat of exhaust steam from a turbine todehydrate and upgrade a bituminous froth or emulsion concurrently withthe effrcient operation of a steam turbine power plant.

The invention disclosed herein is concerned with the efficientproduction of synthetic petroleum oil and other petroleum derivativesfrom a source such as shale oils or more preferably tar sands. The tarsands are a particularly desirable source of petroleum derivativesbecause extensive deposits are found on the North American Continent,principally in the Athabasca District of the Province of Alberta inCanada.

Typically, these sands contain about 6 percent to about 20 percent of ahydrocarbon material called bitumen (also referred to herein as oil),from about 1 percent to about 10 percent water, and from about 70percent to about 90 percent of various mineral solids. The specificgravity of bitumen varies from about 1.0 to about 1.05 and the bitumenhas an API gravity of about 8.0 (at 60 F The major portion, by weight,of the mineral solids in the bituminous sand is quartz sand havingparticle size varying generally between about 45 microns and 2,000microns. Various other mineral inclusions are also found in thebituminous sand such as clay and silt fines of a particle size belowabout 45 microns.

Several methods are known or have been proposed for separating the oilfrom the bituminous sand. Some of these methods involve the use of waterfor preparing an aqueous slurry of the tar sand at a temperature above75 F., in order to encourage dispersion and separation of the mineralsolids from the bitumen. Most of the quartz sand and portions of thetines are separated from the slurry by various mechanical means,principally flotation separation of the bitumen as an emulsion. Thebituminous emulsion or froth which is recovered from the primaryseparation contains some tine sand particles and a small quantity ofcoarse sand. Typically, the bituminous emulsion contains from about 10percent to 60percent water, percent to 20 percent minerals mostly fines,from about 30 percent to 85 percent bitumen, and is subsequentlysubjected to various mechanical dewatering operations such as mechanicalagitation to coalesce the water, and roller dewatering in order toreduce the water content to a minimum.

However, it is generally necessary to reduce the water content of thebitumen to as small an amount as possible, before subjecting the bitumento various petroleum processing steps. Generally, it is thereforepreferred to substantially fully dehydrate the bituminous emulsion andthereby substantially reduce water content of the oil product.

I have invented a method for recovering bitumen from bituminous emulsionof the type described above. More particularly the process contemplatesintegration of a steam power generation'process with thermal dehydrationof a bituminous emulsion in the production of a synthetic crude oil. Thelatent heat of the exhaust steam from the steam turbine provides heatfor the thermal dehydration of the bituminous emulsion, whilesimultaneously acting to condense the exhaust steam. The processtherefore comprises heating a stream of bituminous emulsion with thelatent heat from exhaust steam to vaporize water and low boilingmaterial contained in the emulsion, while simultaneously condensing theexhaust steam, and separating the vaporized water from the bituminousemulsion. The process additionally comprises further heating theseparated bituminous emulsion by heat transfer from the exhaust steam tovaporize essentially all the remaining water in the bituminous emulsion,separating the vaporized water from the bitumen stream, and returningthe condensed water from the exhaust steam to the steam power plant.

It is therefore an object of this invention to provide an improvedprocess for the thermal dehydration of bituminous emulsion.

Another object of this invention is to provide an effcient process forboth the thermal dehydration of bituminous material, and the efiicientproduction of energy.

Still another object of this invention is to provide an integratedprocess for the heating and dehydration of the bituminous emulsion whilesimultaneously condensing the exhaust steam from a steam turbine powerplant, and returning the condensate to the power plant.

Other objects and advantages of the process of this invention willbecome apparent to those skilled in the art from the description of thedrawings and preferred embodiments which follow.

The drawing shows in schematic form the process of this invention.

More particularly, the drawing shows a stream of bituminous emulsionfrom a primary separation vessel (not shown) being fed into a retentiontank 12 where the emulsion is retained for a period of time generallybetween 1 and 10 days so as to allow some of the water contained in theemulsion to coalesce. The stored emulsion is then passed over a seriesof mechanical dewatering rollers 14 which act to remove a fraction ofthe water contained in the emulsion by allowing the bituminous emulsionto adhere to the surface of the rollers and be removed by the doctorblades 'or similar means while coalesced water not adhering to'therollers is drained away from the rollers. The rollers dewateredbituminous emulsion which contains from about'20 to '30 percent water isnext subjected to thermal dehydration. The use of roller dewateringserves to provide effective means for reducing the water con-. tent ofthe bituminous emulsion to a relatively constant level so as to providea relatively uniform stream of bituminous emulsion as feed for thermaldehydration.

The bituminous emulsion feed after being dewatering is preferably heatedto -200 F.) in a storage tank 16 and passed via a bituminous feed pipe18 and feed pump 20 to a predehydration'heat exchanger 22. The feed pumpraises the pressure of the preheated'bituminousemulsion to about 30p.s.i.g. prior to entering the predehydration heat exchanger 22. In thepredehydration heat exchanger 22, the temperature of the bituminousemulsion stream is raised by heat transfer from the heating fluid to atemperature at which water contained in the emulsion stream (at' theraised pressure) will vaporize. Where a stream pressure of about 50p.s.i.g. is maintained, it is preferred that the bituminous emulsiontemperature be raised in the predehydration heat exchanger to atemperature of about 275 F. The stream of heated emulsion from thepredehydration heat exchanger 22 is then passed to a first dehydrationvessel 24 where the vaporized material is separated from the bituminousemulsion stream. A major portion of the vaporized material, principallywater, but also including low boiling hydrocarbon material, is removedfrom the first dehydration vessel 24 via an effluent venting conduit 26and passed to a contact condenser 28 where it is condensed by mixing itwith cooling water from a source not shown. The mixture of cooling waterand the condensate is then passed to oil-water separator 30 where lightgas-oil is separated therefrom.

The partially dehydrated bitumen stream from the first dehydrationvessel 24 is passed via conduit 32 to an interdehydration heat exchanger34 where the bituminous emulsion is heated as hereinafter described to ahigher temperature. .The temperature to which the bituminous emulsion isheated in the interdehydration heat exchanger 34 is deter mined by themaximum temperature at which the heating fluid is supplied to theinterdehydration heat exchange and by the economics of the integratedpower plant and thermal dehydration process. Basically, the temperatureto which the partially dehydrated bituminous emulsion is raised in theinterdehydration heat exchanger is limited by the available temperatureof the heating fluid, that is the exhaust steam. The heating of thebituminous emulsion stream in the interdehydration heat exchangersubstantially vaporizes all the remaining water in the emulsionincluding some hydrocarbon material.

The heated bituminous emulsion stream is then passed to a seconddehydration vessel 36. The second dehydration vessel 36 is maintained ata similar pressure to that of the first dehydration vessel allowing forany pipe resistance losses and process losses. Material boiling belowthat pressure and temperature are therefore in the vapor phase in thesecond dehydration vessel and are efi'ectively separated from the steamof liquid bituminous material. The vaporized material is passed fromvessel 36 via a conduit 38 to the contact condenser 28 where it istreated as hereinbefore described. The second dehydration step in thevessel 36 serves to remove most of the remaining water present in thebitumen stream.

The fully dehydrated bitumen stream from the second dehydration vessel36 is then passed through a pump 40 to a postdehydration heat exchanger42 preparatory to processing the bitumen stream for the removal ofsolids and the separation of gas oil and naphtha.

The fully dehydrated bitumen stream is heated to a higher temperature inorder to reduce its viscosity prior to removing solids by cycloning. Thepressure and the temperature of the fluid during cycloning determinesomewhat the amount of solids which will be removed from the stream.Accordingly, it is desirable to reduce the viscosity since this does infact increase the recovery or removal of solids from the stream.Therefore, the dehydrated bitumen stream is heated to about 575 F., inthe postdehydration heat exchanger 42 and passed through a surge tank 44where hydrocarbon material boiling below 575 F. at the particularpressure i.e. 50 p.s.i.g. is vented off. The remaining high boilinghydrocarbon material is then passed through a series of cycloneseparators 46, one of which is shown and which functions as described inU.S. Pat. No. 3,383,814 issued on Aug. 29, 1967 to R. A. Given et al.disclosing a process for separating oil from bituminous sand.

Heat for dehydrating the bituminous stream and for preparing thedehydrated bitumen stream for cycloning is obtained by utilizing thelatent heat available in the exhaust steam turbine 60 operated as partof an electrical power generating plant (not shown). The power plant isnecessary to provide electrical power for the operation of the completetar sand processing facility. Ordinarily the power plant process wouldbe substantially complete cycle of operations in itself, receiving fueland cooling water as outside inputs and generating electrical power andpossibly steam for use elsewhere. Except for steam generated for useelsewhere for heating purposes, the exhaust steam from the turbine wouldordinarily be condensed utilizing available coolants, preferably riveror lake water, before being recycled to the steam boilers for reheatingto high temperature, high pressure steam. Feed water which issatisfactory for conversion to and use as steam in a steam turbine mustmeet stringent purity and chemical standards and therefore it isincumbent upon those designing and operating a steam power plant thatfeedwater loss be maintained at a minimum. Finally, to achieve anefficient use of the steam turbine, the back pressure of the steamturbine condenser must be kept at a minimum in order to reduce thetemperature at which the steam would cease to be superheated and becomewet. The above described parameters contribute to the difficulty ofutilizing the steam generated in the operation of the power plant forany major use other than powering the steam turbine.

More particularly the drawing shows the steam turbine 60, preferably aconventional back pressure steam turbine, receiv ing high temperatureand high pressure steam from a steam generator such as a boiler 64, andexhausting spent steam at above atmospheric pressure and relatively hightemperature (i.e. a temperature above the boiling point of water at thatexhaust pressure) to an exhaust conduit 66 and back to the boiler 64where the exhaust steam is reheated to somewhat a higher temperature.The steam turbine 60 is operated without a condenser at its exhaust end,resulting in exhaust steam which is dry at exhaust pressure. While theexhaust steam may if desired be used solely for the dehydration of thebituminous emulsion, it is particularly preferred that the steam also beutilized to heat the dehydrated bitumen stream for further processing asdescribed above. The exhaust steam from the turbine 60 is passed throughthe exhaust conduit 66 to a reheater 68 mounted in the boiler 64 byopening a reheat valve 70 mounted in the exhaust conduit 66. Aconnecting valve 72 is mounted in a connecting conduit 74 which connectsthe exhaust conduit 66 directly to a main steam line 76. The main steamsupply line 76 is connected at one end to the high temperature side ofthe reheater 68 and at the other end of the postdehydration heatexchanger 42. A valve 78 is mounted in the main steam supply line 76between the reheater 68 and the junction between the connecting conduit74 and the main steam supply line 76 between the reheater 68 and thejunction between the connecting conduit 74 and the main steam supplyline 76. By opening valves 70 and 78 and closing connecting valve 72,reheated exhaust steam is supplied to the dehydration process via themain supply line 76. Alternatively exhaust steam directly from the steamturbine is supplied to the process by closing closing valves 70 and 78and opening valve 72.

Reheated exhaust steam is supplied to the postdehydration heat exchanger42, where it serves to raise the temperature of the fully dehydratedbitumen stream to that necessary for effective subsequent processingsuch as cycloning.

The heating fluid, that is the steam leaving the postdehydration heatexchanger 42, is passed to the interdehydration heat exchanger 34 viaconduit 82. The steam entering the interdehydration heat exchanger 34 ispreferably at sufficiently high temperature to transfer enough heat(B.t.u./lb.) to raise the temperature of the bituminous emulsion steampassing through the interdehydration exchanger to about 350 F.Alternatively, steam may be sup lied to the interdehydration heatexchanger 34 directly from the main supply line 76 rather than from thepostdehydration heat exchanger 42. For this purpose a bypass conduit 80is directly connected between the steam supply line 76 and conduit 82which carries the steam from the postdehydration heat exchanger 42 tothe interdehydration heat exchanger 34. Suitable valves are located inthe bypass conduit and the steam lines to and from the postdehydrationheat exchanger. Valve 83 is mounted in the bypass conduit 80 and whenopen allows steam to pass directly to the interdehydration heatexchanger from the main steam supply line 76. Valves and 84 are mountedrespectively in the steam piping to and from the postdehydration heatexchanger, valve 84 being mounted in conduit 82, and valve 85 in themain steam supply line 76 between conduit 80 and the postdehydrationheat exchanger.

The exhaust steam after passing through the interdehydration heatexchanger 34 is passed to the predehydration heat exchanger 22 whereheat from the exhaust steam is initially transferred to the bituminousemulsion stream. The bituminous emulsion stream as it passes through thepredehydration heat exchanger 22 is heated to at most the temperature ofthe heating fluid stream leaving the interdehydration heat exchanger 34.The utilization of the predehydration heat exchanger 22 and the firstdehydration vessel allows a significant portion of the water and lowboiling hydrocarbon material to be vaporized and separated from thebituminous emulsion stream before having to. raise the temperature ofthe partially dehydrated emulsion stream in order to vaporize theremaining water. This accounts for a significant saving in heat energyfor the process, since it is not necessary to heat the water and lowboiling material previously removed in the first dehydration vessel.

Finally, the exhaust steam from the predehydration heat exchanger 22 ispassed to a trim exchanger 86 where partially treated water is heated byheat transfer from the exhaust steam and converted to low temperaturesteam at about 50 p.s.i.g. for subsequent use in various extractionprocess requirements such as heating the tar sand slurry duringextraction and separation. Since this water is not used as feed for thepower plant, it need not be purified to the extent necessary for powerplant feed water. The condensed exhaust steam or rather more explicitlythe condensate from the trim exchanger 86 is returned via condensatefeed conduit 88 back to the boiler 64 for use as feedwater.

While the invention has been described with reference to one of thepreferred embodiments, another embodiment also contemplated as part ofthe invention, and utilizing thesystem described above is as follows.The exhaust. steam is.passed directly from the turbine 60 to theinterdehydration heat exchanger 34. For this particular type operation,the valves 70 and 78 are closed, valves 72 and 83 are opened, and thevalves 84' and 85 leading to and from the postdehydrationheat exchanger42 are closed. Exhaust steam is thereby exhausted directly from theturbine 60 to the interdehydration heat exchanger 34 without reheating.The exhaust steam is subsequently" utilized in the same manner ashereinbefore described to act as a heating fluid for dehydrating thebitumen stream according to'the present invention.

With a view of illustrating the. present invention but not as alimitation thereon, the following examples are given.

EXAMPLE I 990 lbs/hr. of a bituminous emulsion stream containing byweight about 71% oil, about 23% of .water, and about 6% solids arepreheated to about 150 F. and pumped at a pressure of about 30 p.s.i.g.to the predehydration heat exchanger 22. Likewise 730 lbs. per hour "ofsteam at a pressure of 100 p.s.i.g, and a temperature of 460 F. isexhausted from the turbine' 12. The exhaust steam therefore has anenthalpy (h) of about 126 B.t.u./lb. The exhaust steam is passed to thesteam reheater 68, reheated to a temperature of about 710 F., therebyincreasing in enthalpy to about 1375 B.t.u./lbs. The process is operatedas described above and the energy transfer between the bituminous streamand the exhaust steam is as follows.

POSTDEHYDRATION HEAT EXCHANGER 42 Heat Transferred-83,500 B.t.u./hr.

SteamtHeating Fluid) Bituminous Emullion Man 730 lbsJhr. 745 lblJhr.*Temp. (T) in 7l0' F. 350' F. Temp. (T) out 465' F. 575' F. Preuure l00p.l.i. 50 p.|.i.g. it out I259 B.t.u./lbs.

INTERDEHYDRATION HEAT EXCHANGER 34 Heat Transferred-48,900 B.t.u./hr.

Stclmtfleating Fluid) Bltuminoul Emulsion Thus a total of about 240B.t.u. per lbs. is extracted from the reheated exhaust steam andutilized in upgrading and dehydrating bituminous emulsion stream. Thisrepresents a utilization of about 7kilowatt hour (kw. hr.) per lbs. ofexhaust steam.

EXAMPLE u The same fiow rates of 'steamand the bituminous emulsionstreams were processed according to the present invention, however, theexhaust steam was neither reheated nor passed 1 directly to thepostdehydration heat exchanger. Rather, the

exhaust steam was passed directly to the interdehydration exchanger 34.As such the details given in example I for the interdehydration andpredehydration heat exchangers are appressure condenser. Furthermore,the process according to either examples I or ll effectively reduced thewater content of the bituminous stream from about 23%to below one tenthof one percent.

Accordingly having described the invention and wishing to coverthose'modifications and advantages which would be apparent to thoseskilled in the art without departing from the spirit and scope of theinvention,

I claim:

1. A process for dehydrating a bituminous emulsion utilizing exhauststeam, said exhaust steam being at a temperature of about 460 F. and apressure of about p.s.i., said process comprising first cooling saidexhaust steam by indirect heat transfer in a second'heat transfer zoneto a partially dehydrated bituminous emulsion stream, said indirect heattransfer indirectlyzheating said partiallydehydrated emulsion to atemperature of about 3'50 F., thereby substantially vaporizing anyremaining water in said partially dehydrated emulsion,

separating said vaporized water from said heated partially dehydratedbituminous stream, thereby obtaining a dehydrated bituminous stream anda cooled exhaust steam, further cooling said cooled exhaust steamby'indirect heat transfer to .said bituminous emulsion in a first heattransferzone, said cooled exhaust steam thereby first indirectly heatingsaid bituminous emulsion in said first heat transfer zone to atemperature sufficient topartially vaporize water from said first heatedemulsion, and

separating said partially vaporized water from said first heatedemulsion thereby obtaining said first partially dehydrated bituminousemulsion stream.

2. A process for dehydrating a bituminous emulsion'utilizing exhauststeam, said exhaust steam'being at a temperature of about 460 F. and apressure of about l00 p.s.i., said process comprising first cooling saidexhaust steam by indirect heat transfer in a secondheat transfer zone toa partially dehydrated bituminous emulsion stream, said indirect heattransfer indirectly heating said partially dehydrated emulsion to atemperature of about 350 F., thereby substantially vaporizing anyremaining water in said partially dehydrated emulsion,

separating said vaporized water from said heated partially dehydratedbituminous stream, thereby obtaining a dehydrated bituminous stream anda cooled exhaust steam,

further cooling said cooled exhaust steam by indirect heat transfer tosaid bituminous emulsion in a first heat transfer zone, said cooledexhaust steam thereby first indirectly heating said bituminous emulsionin said first heat transfer zone to a temperature of about 275 F. to

exhaust temperature,

further heating said dehydrated bituminous stream by indirectlytransferring heat from said reheated exhaust steam in a third heattransfer zone to the dehydrated bituminous stream, and

cycloning the heated, dehydrated bituminous stream,

thereby removing solids therefrom.

2. A process for dehydrating a bituminous emulsion utilizing exhauststeam, said exhaust steam being at a temperature of about 460* F. and apressure of about 100 p.s.i., said process comprising first cooling saidexhaust steam by indirect heat transfer in a second heat transfer zoneto a partially dehydrated bituminous emulsion stream, said indirect heattransfer indirectly heating said partially dehydrated emulsion to atemperature of about 350* F., thereby substantially vaporizing anyremaining water in said partially dehydrated emulsion, separating saidvaporized water from said heated partially dehydrated bituminous stream,thereby obtaining a dehydrated bituminous stream and a cooled exhauststeam, further cooling said cooled exhaust steam by indirect heattransfer to said bituminous emulsion in a first heat transfer zone, saidcooled exhaust steam thereby first indirectly heating said bituminousemulsion in said first heat transfer zone to a temperature of about 275*F. to partially vaporize water from said first heated emulsion, andseparating said partially vaporized water from said first heatedemulsion thereby obtaining said first partially dehydrated bituminousemulsion stream.
 3. The process of claim 1 in which the bituminousemulsion contains solids, and which additionally comprises firstreheating the exhaust steam to a temperature above the exhausttemperature, further heating said dehydrated bituminous stream byindirectly transferring heat from said reheated exhaust steam in a thirdheat transfer zone to the dehydrated bituminous stream, and cycloningthe heated, dehydrated bituminous stream, thereby removing solidstherefrom.